Locating device



R E N F F 0 F LOCATING DEVICE Filed Nov. 3, 1944 3 Sheets-Sheet 1 I l l I Wd . MM. 0 M 1 mu 2 i Z w mu Z w F. OFFNER LOCATING DEVICE Aug. 8, 1950 3 Sheets-Sheet 2 Filed Nov. 5, 1944 Common Luff El?! Aug.8, 1950 F. QFFNER 2,517,702

LOCATING DEVICE Filed Nov. 3, 1944 3 Sheets-Sheet 3 Patented Aug. 8, 1950 UNITED STATES PATENT OFFICE 2,517,702 LOCATING DEVICE Franklin Oflner, Chicago, Ill.

Application November 3, 1944, Serial No. 561,783

4 Claims. (01. 343-118 This device relates to the location of objects by means of radiant energy, particularly infra-red radiation, emitted or reflected by the objects.

A principal purpose of the invention is the provision of a device for the location of objects.

A further purpose of the device is the provision of means for locating the direction of a source of radiant energy.

Another purpose of the invention is the provision of a device for causing radiant energy from a distant object to generate a pulsating electric current varying in phase and amplitude in dependence upon the relative direction of the object.

Another object of the invention is the provision of means for measuring the changing phase and amplitude of electric currents.

The apparatus of the invention comprises detector means, including a radiation sensitive element, for producing electric current variations in response to variations in radiation incident on. the element, means for cyclically varying the incidence of radiation on the element in fixed phase relation to the direction of the source of radiation, directional indicating means responsive to the output of the detector means, and switching means for impressing the output of the detector means on the indicating means in a sense cyclically varying in synchronism with the radiation varying means.

The radiation sensitive element of the apparatus of the invention may be any or a number of known elements of this type, such as a photoelectric cell, a radio antenna, a radiation thermopile, a radiation bolometer, or the like. The thermopile and the bolometer are especially useful in locating objects by means of far infra-red radiation (heat rays).

The principles of the invention will be more particularly described with reference to apparatus including radiation bolometers as the radiation sensitive element, as shown by way of illustration in the accompanying drawings in which:

Fig. 1 is a diagrammatic representation of apparatus embodying the principles of the invention as applied to radiation bolometers;

Fig. 2 is a diagram of optical and voltage patterns typical of the apparatus of Fig. 1;

Fig. 3 is a detailed electric circuit diagram of a typical arrangement of electrical apparatus elements of the invention, and 1 Figs. 4, 5 and 6 are partial diagrammatic representations showing the application of the invention to photoelectric cells, radiation thermopiles and radio antennae, respectively.

In Fig. 1, I0 is a radiation bolometer typically comprising blackened thin nickel strips I I, placed behind a circular aperture i2, and mounted in case 35. When radiation falls on the strips, a temperature change will occur, which may be detected by the change in electrical resistance.

The 'bolometer is placed at the focus of a parabolic reflector it. The reflector is mounted on a rotating shaft ll, driven by motor 34, the bolometer being mounted axially. with the shaft. The reflector is mounted slightly eccentrically on the shaft, so that as the shaft and reflector rotate the image of a distant small object lying along the axis will trace out a circular path falling on the rim of the circular aperture of the bolometer. The image of objects offthe axis will then also trace nearly circular patterns, but intersecting the bolometer aperture in a phase dependent upon the direction of said object. This is illustrated in Fig. 2, wherein A illustrates the path of the image for object on axis; B, object at left; C, object at right; D, object down and left.

Current from a battery It is passed through the bolometer elements H, and primary winding lBa of transformer i8. (The circuit is shown in a simplified form in Fig. 1.) As radiation falls on the bolometer, the variation in its resistance modulates the current flow, producing an amplified voltage at the secondary lSb of IS. The phase of this voltage varies directly with the phase at which the image crosses the aperture; the phase of the voltage thus determines the angular position of the object in the field. This is illustrated in Fig. 2, typical wave forms being illustrated for the various object positions shown; with the object centered, Fig. 2-A, no output voltage is (theoretically) obtained.

As the voltage obtained from the secondary of It may still be minute, it is amplified by electron tube amplifier II. The output of i1 is arranged to provide symmetric positive and negative signals. That is, when output terminal II has ten volts positive signal with respect to neutral point 20, output terminal l9 has ten volts negative signal. The output signal is fed through a synchronous switch 2 I, operated by shaft l4, synchronously with the rotation of reflector l3. Switch 2i may be made in the form of a slip ring and commutator, as illustrated. Slip-ring 22 is connected to amplifier output terminal 89 through brush 24; slip-ring 23 is connected to terminal l8 through brush 25. Half of each slip-ring is half cut away and over-lapped, to form a commutator. Brushes 26 and 21 are disposed at 90 along the commutator. Then brush 26 will be connected to terminal I8 for half of each revolution of the commutator, and to I! for the other half. Brush 21 will be similarly connected, but will be switched in 90 rotation after 28. Each brush is connected to a resistance-capacity averaging circuit 28-49 and Bil-3|, and voltage measuring means 32 and 33. The action of the switching and measuring circuits is illustrated by the bars below the wave form curves of Fig. 2. The vertical bars refer to brush 26; the horizontal to 21. The shaded bars indicate that the corresponding brush is connected to terminal l3, and the white bars indicate connection to terminal i9. In Fig. 2--B, the horizontal brush is connected to terminal l3 while I3 is positive; one-half cycle later, when i3 is negative, the brush is connected to i3 which is now positive. The averaging circuit provides a relatively uniform voltage to measuring means 32; this, then, indicates a positive voltage. positive reading on 32 thus indicates "object on left."

Observing now the voltage applied to the vertical brush 23, it is seen that half thev time it is connected to I3, I3 is positive, and the other half negative; and that the average is zero, and similarly while connected to l3. Thus the .average voltage measured at 33 is zero, indicating "object centered" for vertical.

With the object to the right, Fig. 2--C, a similar analysis shows 32 will give a negative indication and 33 again zero.

With the object left and down, Fig. 2-D, 32 will be positive (although it will not show maximum positive voltage), and 33 will also be posi-. tive. Thus the polarity shown by 32 and 33 will indicate the quadrant position of the object.

Voltages varying at frequencies other than synchronous with the commutator will be averaged out in a sufilcient number of cycles; except that odd order harmonics of the commutator frequency will be passed, although attenuated. The averaging time oi the circuit depends upon the product of resistor 23 and capacitor 23, and resistor 33 and capacitor 3|. This product determines the selectivity characteristics of the circuit. The greater the product, the greater the selectivity and the greater the discrimination that the circuit will provide against undesired frequencies. This discrimination is of importance in a locating device as the limit of sensitivity is usually provided by undesired random voltages. The selectivity provided therefore reduces the efi'ect of such undesired voltages making possible increased sensitivity.

The complete electrical circuit embodying the principles of the invention is shown in Fig. 3. 3 is the bolometer, 4| is a resistor having resistance equal to the resistance. of i3. These are connected across a transformer 42 having a center-tapped primary 43. The voltages for energizing I3 is introduced through the center-tap of 43, and through current limiting resistor 43. The purpose of 4| in conjunction with the centertapped winding 43 is to provide equal currents through both halves of 43, the net magnetic efiect cancelling. This prevents saturation effects in the core of 42. The varying radiation falling on I3 as the reflector rotates causes a variation in the resistance of [3 with a consequent variation in the current through 43. This induces an increased voltage variation in the secondary winding 44; 44 having many times the number of turns of wire in 43.

The voltage produced by 44 is amplified in pentcde amplifier tube 43. This has conventional cathode resistor bias 46, with by-pass condenser 41; screen resistor 43, with by-pass condenser 43; and plate load resistor 33.

The output of the first stage of amplification is coupled to the next stage by condenser 3|, and grid return resistor 32. 32 is made variable for a reason to be disclosed below. The-connection to the following amplifier tube 34 is made through current limiting resistor 33. The purpose of this resistor is to limit the grid current which may iiow during large positive signal voltages.

34 is a dual triode. A signal is applied to the grid of only one triode, the other grid being connected to a constant voltage. A degenerative signal is produced across the common cathode resistor 33, which results in substantially equal signals being developed across each load resistor 33 ,and 31. It will be noted that the grid return to each triode section is made to a positive voltage; the bias developed across" is sufiicient to provide a net negative bias to the grids. The output of this second stage of amplification is coupled into a third stage through condensers 33 and 33, followed by grid coupling resistors 33 and 3|, and current limiting resistors 32 and 33. The third stage is again a dual triode 34, having a common cathode resistor 33. The plate resistors are 33 and 31. This is coupled into a fourth stage of amplification, another dual triode 14, through condensers 33, 33; grid return resistors 13, 1|; and grid current limiting resistors 12, 13. i3 is a common cathode resistor; 13, 11 the plate load resistors.

The output of the final stage of amplification is coupled into the synchronous switch 2|, through condensers 13, 13 and resistors 33, 3|. The synchronous switch, which is shown in more detail in Fig. 1, consists of twostepped sliprings 22, 23 mounted on, but insulated from, the shaft which carries the reflector. The brushes 24, 23, 23 and 21, as previously described, switch the output terminals l3, IQ of the amplifier, to the averaging networks 23, 23 and 33, 3|. The measuring means 32 and 33 are here provided by a dual triode vacuum tube 32. In the plate circuit of one section is relay 33,-and in the other section relay 34. A negative bias voltage is provided for 32 through battery 33. With this bias voltage, if a positive voltage accumulates on condenser 3|, relay 33 will close contacts 33, 31, giving an up indication; if a negative accumulates on 3|, the relay 33 opens, opening contact 33, 31, and closing contact 33, 33, giving a down indication. Similarly, if a positive charge accumulates on 23, contacts 33, 33 are closed by relays 34, giving a right indication, while if a negative charge accumulates on 23, contacts 83, 33 are opened and 33, 3| closed, giving a left indication.

' If a large positive current flows, for example, through 33 into 3|. the voltage on 3| would tend to take 'on a large positive value. It is, however, limited by the grid current of 32 to a voltage (as measured from the negative end of 33) approximately equal to the voltage of 33. The double dio'de 32 is provided to limit the maximum negative voltage which may be accumulated by 23 and II. This double diode has its plates biased negatively by 33 to an amount approximately double the bias provided by 33. Then the negative voltage accumulating on 23 or 3| cannot appreciably exceed the voltage provided by 33. The plate voltage supply of the first two stages is'provided by battery 34. The plate voltage aupply of the second two stages of amplification, as well as the relay tube 32, is provided by battery 33. A tap on 34 provides the positive bias voltage for 34. 34, 14. The voltage for the bolometer circuit is provided by battery 33. This battery alsosupplies the voltage for the heaters .of vacuum tubes 43, 34, 34, 14, 32 and 32 through to circuit elements, not shown. Resistor 32 is made variable to adjust the phase shift of the amplifier. Because of the thermal lag of the bolometer there will be a phase shift in the voltage developed thereby in comparison with the radiation falling 15 thereon. The phase'shift of the amplifier may be made equal and opposite thereto by adjusting 52. If the phase shift is so adjusted, the rate 01' change of phase shift with the speed at which the reflector is driven will be approximately equal and opposite for the amplifier and bolometer, so that the net phase shift will be approximately zero for speeds in the vicinity for which 52 is adiusted. This eliminates the needfor close control 01' the speed of the motor, while maintaining the accuracy with which the vertical and horizontal axes are defined.

While this apparatus has been particularly described with reierence' to a bolometer, it may also be used with other sources 01' radiation. For example, in the input circuit consisting of i0, 4|, 42, 43, 44, 45 01' Fig. 3, the bolometer l may be replaced by a photoelectric cell I 09,.as illustrated in Fig. 4; or a thermopile I08, as illustrated in Fig. 5; or a radio receivingantenna I I0,

1|! the tuning condenser, ll 9 a rectifier-detector,

and I ll a radio-frequency choke coil.

The advantages discussed with respect to Figs.

1-3. would accrue in. all these illustrative examples.

While the invention has been illustrated for circular scanning, it can be applied equally well to any other form of repetitive scanning pattern. For example, it may be applied to a linear scanning method wherein the reflector 13 instead of rotating eccentrically is oscillated back and forth, producing a linear scanning pattern. The synchronous switching arrangement is then synchronized with the linear oscillations of the reflector rather than with the circular oscillations as in the above description.

It will be obvious that the signals impressed on the indicating means of the invention may be utilized through current or voltage sensitive devices of known type for directional control purposes and the invention includes the apparatus defined in the claims hereof when the direction indicating signals are so utilized, in which case the response or the controlled device to the signals may be the sole directional indication.

I claim:

1. In combination, an infra-red radiation sensitive element producing electrical current variations in, response to variations in incident radiation, means for cyclically varying the radiation on said element, current translating means connected to said element, switching means synchronous with said radiation varying means connected to output of said translating means, current sensitive means connected to said switching means, and means for adjusting the phase shift of said current translating means to compensate ior phase shift in said sensitive element.

2. In combination, an infra-red radiation sensitive element producing electrical current variations in response to variations in incident radiation, means for cyclically varying the radiation on said element, current translating means connected to said element, said translating means providing two symmetrically varying output voltages of opposite polarity, switching means synchronous with said radiation varying means. resistance-capacity averaging means connected by said switching means to one said symmetri- 6 cally varying output voltage during one-half of each cycle of radiation variation, and to the other said voltage during the opposite half of each cycle, and voltage sensitive means connected to said averaging means.

3. In combinatioman infra-red radiation sensitive element producing electrical current variations in response to variations in incident radiation, means for cyclically varying the radiation on said element, current translating means connected to said element; said translating means providing two symmetrically varying output voltages of opposite polarity, switching means synchronous' with said radiation varying means,

resistance-capacity averaging means connected by said switching means to one said symmetrically varying output voltage during one-half of each cycle of radiation variation, and to the other said voltage during the opposite half of each cycle, voltage sensitive means connected to said averaging means, and a second averaging means connected as the firstsaid averaging means, together with associated voltage sensitive means. switchin of said second averaging means occurring at a phase displacement from switching of said first averaging'means.

4. In combination, an infra-red radiation sensitive element producing electrical current variations in response to variations in incident radiation, means for cyclically varying the radiation on said element, current translating means connected to said element, said translating means providing two symmetrically varying output voltages of opposite polarity, switching means synchronous with said radiation varying means, resistance capacity averaging means connected by said switching means to one said symmetri-- cally varying output voltage during one-half of each cycle of radiation variation, and to the other said voltage during the opposite half or each cycle, voltage sensitive means connected to said averaging means, and a second averaging means connected as the first said averaging means,

together with associated voltage sensitive means, switching of said second averaging means occurring at a phase displacement oi substantially I degrees from switching of said first averaging means.

FRANKLIN OFFNER.

, nmamvcns crrnn The following references are of record in the file of this patent:

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